Question: If $7a + 9b = -8$ and $x + 3y = 1$, what is $-2x - 27b - 6y - 21a$ ?
Solution: $= -21a - 27b - 2x - 6y$ $= (-3) \cdot (7a + 9b) + (-2) \cdot (x + 3y)$ $= (-3) \cdot (-8) + (-2) \cdot (1)$ $= 24 - 2$ $= 22$